Process for producing ethylene/alpha-olefin copolymer

ABSTRACT

A copolymer of ethylene and an alpha-olefin having an ethylene content of from 30 to 90 mole %, a number average molecular weight of from 300 to 30,000 and a molecular weight distribution defined by a Q value (the ratio of the weight average molecular weight to the number average molecular weight of not more than 3 and a Z value (the ratio of the maximum value of the molecular weight to the minimum value of the molecular weight when the molecular weight is measured by gel permeation chromatography) of from 15 to 200. The said copolymer can be produced by a process comprising copolymerizing ethylene with an alpha-olefin in the liquid phase in the presence of a polymerization catalyst composed of a combination of a soluble vanadium compound and an organoaluminum compound in the co-presence of hydrogen, characterized in that 
     (a) the copolymerization is carried out in a continuous manner, 
     (b) the concentration of the vanadium compound in the polymerization system is maintained at 0.3 to 30 millimoles/liter, and 
     (c) the vanadium compound is supplied to the polymerization system as a solution in a polymerization medium in a concentration which is 1 to 5 times the concentration of the vanadium compound in the liquid phase. This compound is useful as a synthetic lubricant oil, a fuel oil additive and a lubricant oil additive.

This application is a continuation of application Ser. No. 07/825,842,filed Jan. 28, 1992, now abandoned; which is a continuation ofapplication Ser. No. 07/567,108, filed Aug. 14, 1990, now abandoned;which is a division of application Ser. No. 07/364,535, filed Jun. 12,1989, now abandoned; which is a continuation of application Ser. No.07/220,954, filed Jun. 23, 1988, now abandoned; which is a continuationof application Ser. No. 06/885,399, filed Jul. 18, 1986, now abandoned;which is a continuation of application Ser. No. 06/770,019, filed Aug.29, 1985, now abandoned; which is a continuation of application Ser. No.06/553,873, filed Nov. 21, 1983, now abandoned; which is a continuationof application Ser. No. 06/338,138, Jan. 8, 1982, now abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a novel ethylene/alpha-olefin copolymer. Morespecifically, it relates to an ethylene/alpha-olefin copolymer having alow molecular weight and a relatively narrow molecular weightdistribution, a process for its production, and its use as a syntheticlubricant oil, a fuel oil additive and a lubricant oil additive.

2. Description of the Prior Art

It is known that an ethylene/alpha-olefin copolymer having a lowmolecular weight which is useful as a synthetic lube oil is obtained bycopolymerizing ethylene with an alpha-olefin having at least 3 carbonatoms in the liquid phase in the presence of a catalyst composed of acombination of a soluble vanadium compound and an organoaluminumcompound in the co-presence of hydrogen (see U.S. Pat. No. 3,851,011).When the copolymer is produced by the method specifically disclosed inthe Example of this U.S. Patent, it has poor uniformity (namely, it hasbroad molecular weight and composition distributions and sometimes it isobtained as a milky liquid or a white paste). When the product obtainedhas a low viscosity, it does not have a high flash point as a lubricantoil unless a low-molecular-weight portion is removed. On the other hand,if a product having a high viscosity is obtained, it has an excessivelyhigh pour point and is not practical as a lube oil. Oils which have aviscosity at 100° C. of at least 60 centistokes are useful as lube oilsfor high loads. Those copolymers which are disclosed in the above Patentand have a viscosity in this range have too high a pour point to be usedfor practical applications. The U.S. Patent suggests that the copolymercan be fractionally distilled, and that a product having a narrowboiling point range obtained by fractional distillation can remove theaforesaid defects with regard to pour points and flash points. It isextremely difficult in this case, however, to obtain a product having asatisfactorily high viscosity index.

Japanese Patent Publication Nos. 37237/1975 and 7717/1976 suggestprocesses for producing an ethylene/alpha-olefin copolymer having a lowmolecular weight, and state that the production of copolymers having anarrow molecular weight distribution is possible. These processes,however, have the defect that special compounds must be used as amolecular weight controlling agent or a catalyst promotor. In addition,copolymers having a sufficiently low molecular weight, such as those oflubricant oil grade, which are prepared in accordance with the specificdisclosures of these Patent Publications do not have a sufficientlynarrow distribution of molecular weight, and, therefore, have the samedefects as described above with regard to U.S. Pat. No. 3,851,011.

It is an object of this invention therefore to provide anethylene/alpha-olefin copolymer having a narrow molecular weightdistribution.

Another object of this invention is to provide a process for producingthe aforesaid copolymer in a continuous manner.

Still another object of this invention is to provide a syntheticlubricant oil having a low evaporation loss, a high flash point,excellent low-temperature flowability, good shear stability, goodoiliness, and a high viscosity index.

Yet another object of this invention is to provide a fuel oil havingexcellent low-temperature flowability.

Other objects and advantages of this invention will become apparent fromthe following detailed description.

SUMMARY OF THE INVENTION

According to one aspect of this invention, there is provided a copolymerof ethylene and an alpha-olefin having an ethylene content of from 30 to90 mole %, a number average molecular weight of from 300 to 30,000, anda molecular weight distribution defined by a Q value (the ratio of theweight average molecular weight to the number average molecular weight)of not more than 3 and a Z value (the ratio of the maximum value of themolecular weight to the minimum value of the molecular weight when themolecular weight is measured by gel-permeation chromatography) of from15 to 200.

According to another aspect of this invention, the ethylene alpha-olefincopolymer can be produced advantageously by a process which comprisescopolymerizing ethylene with an alpha-olefin in the liquid phase in thepresence of a polymerization catalyst composed of a combination of asoluble vanadium compound and an organoaluminum compound in theco-presence of hydrogen, characterized in that

(a) the copolymerization is carried out in a continuous manner,

(b) the concentration of the vanadium compound in the polymerizationsystem is maintained at 0.3 to 30 millimoles/liter, and

(c) the vanadium compound is supplied to the polymerization system as asolution in a polymerization medium in a concentration which is 1 to 5times the concentration of the vanadium compound in the liquid phase.

DETAILED DESCRIPTION OF THE INVENTION

The soluble vanadium compound used as one component of thepolymerization catalyst in the above process is a vanadium-containingcompound which is soluble at least partly, and in practice, mostly, inthe polymerization medium used. Generally, it includes compound of thefollowing formula ##STR1## wherein R¹ represents an aliphatichydrocarbon group having 1 to 20 carbon atoms, preferably 1 to 10 carbonatoms, X¹ represents a halogen atom, and n is a number of from 0 to 3.

The aliphatic hydrocarbon group R¹ in formula (I-1) is a linear orbranched alkyl group, such as methyl, ethyl, n-propyl, isopropyl,n-butyl, iso-butyl, sec-butyl, n-pentyl, iso-pentyl, n-hexyl, iso-hexyl,heptyl, octyl; nonyl, decyl, dodecyl, tetradecyl, penta-decyl,heptadecyl, octadecyl, nonadecyl, and eicosyl. Those having 1 to 10carbon atoms are preferred.

Chlorine and bromine are preferred as the halogen atom X¹.

Specific examples of the vanadium compound are given below.

VOCl₃, VO(OCH₃)Cl₂, VO(OCH₃)₂ Cl, VO(OCH₃)₃, VO(OC₂ H₅)Cl₂, VO(OC₂H₅)₁.5 Cl₁.5, VO(OC₂ H₅)₂ Cl, VO(OC₂ H₅)₃, VO(OC₂ H₅)₁.5 Br₁.5, VO(OC₃H₇)₂ Cl, VO(OC₃ H₇)₁.5 Cl₁.5, VO(OC₃ H₇)₂ Cl, VO(OC₃ H₇)₃, VO(On-C₄H₉)Cl₂, VO(On-C₄ H₉)₂ Cl, VO(Oiso-C₄ H₉)₂ Cl, VO(Osec-C₄ H₉)₃, VO(OC₅H₁₁)₁.5 Cl₁.5, VO(Oiso-C₅ H₁₁)Cl₂, VO(Oiso-C₅ H₁₁)₁.5 Cl₁.5, VO(Oiso-C₅H₁₁)₂ Cl, VO(Oiso-C₅ H₁₁)₃, VO(OC₆ H₁₃)Cl₂, VO(OC₆ H₁₃)₁.5 Cl₁.5, VO(OC₆H₁₃)₂ Cl, VO(OC₆ H₁₃)₃, VO(OC₈ H₁₇)₂ Cl, VO(OC₈ H₁₇)₁.5 Cl₁.5, VO(OC₈H₁₇)Cl₂, VO(OC₈ H₁₇)₃, VO(OC₁₀ H₂₁)Cl₂, VO(OC₁₀ H₂₁)₁.5 Cl₁.5, VO(OC₁₀H₂₁)₂ Cl, VO(OC₁₀ H₂₁)₃, VO(OC₁₂ H₂₅)Cl₂, VO(OC₁₂ H₂₅)₁.5 Cl₁.5, VO(OC₁₂H₂₅)₂ Cl, VO(OC₁₂ H₂₅)₃, VO(OC₁₅ H₃₁)Cl₂, VO(OC₁₅ H₃₁)₁.5 --Cl₁.5,VO(OC₁₅ H₃₁)₂ Cl, VO(OC₁₅ H₃₁)₃, VO(OC₁₈ H₃₇)Cl₂, VO(OC₁₈ H₃₇)₁.5 Cl₁.5,VO(OC₁₈ H₃₇)₂ Cl, VO(OC₁₈ H₃₇)₃, VO(OC₂₀ H₄₁)Cl₂, VO(O--C₂₀ H₄₁)₁.5Cl₁.5, VO(OC₂₀ H₄₁)₂ Cl, VO(OC₂₀ H₄₁)₃, VO(OC₂₀ H₄₁)Cl₂, VO(OC₂₀ H₄₁)₃,and VCl₄.

Among these compounds, VOCl₃, VO(OC₂ H₅)Cl₂ and VCl₄ are especiallypreferred.

The organoaluminum compound used with the vanadium compound may be thosewhich are usually employed in the production of ethylene/alpha-olefincopolymers. Generally, they include compounds of the following formula

    R.sup.2.sub.m AlX.sup.2.sub.3-x                            (II)

wherein R² represents an aliphatic hydrocarbon group having 1 to 6carbon atoms, preferably 2 to 4 carbon atoms, X² represents a halogenatom, and m is a number of 1 to 3.

The aliphatic hydrocarbon group R² and the halogen X² in formula (II)may be R¹ and X¹ in formulae (I-a) and (I-b).

Specific examples of the organoaluminum compounds include trialkylaluminums such as (C₂ H₅)₃ Al, (iso-C₃ H₇)₃ Al and (iso-C₄ H₉)₃ Al,dialkyl aluminum halides such as (C₂ H₅)₂ AlCl, (C₂ H₅)₂ AlBr and(iso-C₄ H₉)₂ AlCl, alkyl aluminum sesquihalides such as (C₂ H₅)₁.5AlCl₁.5, (C₂ H₅)₁.5 AlBr₁.5 and (iso-C₄ H₉)₁.5 --Al₁.5, alkyl aluminumdihalides such as (C₂ H₅)AlCl₂, (iso-C₃ H₇)AlCl₂ and (iso-C₄ H₉)AlCl₂,and mixtures of these in arbitrary proportions.

According to the process of this invention, the copolymerization iscarried out in a continuous manner by continuously feeding the catalystcomponents, ethylene, an alpha-olefin, hydrogen and optionally, an inertmedium to the polymerization system (polymerization reactor), andwithdrawing the polymer solution substantially continuously from thepolymerization system.

The copolymerization is carried out in the liquid phase. Thepolymerization medium is preferably a liquid medium inert to thepolymerization reaction. The alpha-olefin may be used in excess to causeit to serve also as the polymerization medium. Examples of the inertliquid medium used for this purpose include aliphatic hydrocarbons suchas butane, pentane, hexane, heptane, octane, decane, dodecane andkerosene; alicyclic hydrocarbons such as cyclopentane,methylcyclopentane, cyclohexane and methylcyclohexane; aromatichydrocarbons such as benzene, toluene, xylene, and ethylbenzene; andmixtures of these.

In performing the process of this invention, the concentration of thevanadium compound in the polymerization system and the manner ofsupplying the vanadium compound to the polymerization system are alsoimportant factors. The concentration of the vanadium compound in thepolymerization system is adjusted to 0.3 millimole to 30 millimoles,preferably 0.5 to 20 millimoles, per liter of the liquid phase. If theconcentration of the vanadium compound is below the specified lowerlimit, the partial pressures of ethylene and the alpha-olefin cannot beso much lowered in order not to reduce the yield of the copolymer perunit amount of the polymerization solvent. Consequently, very highpartial pressures of hydrogen are required in order to obtain copolymersof a low molecular weight, and this is disadvantageous both in equipmentand operation. If the partial pressure of ethylene or the alpha-olefinis lowered in order to avoid high hydrogen pressures, a copolymer havinga low molecular weight can be produced under relatively low pressures,but the yield of the copolymer per unit weight of the polymerizationsolvent is low. Hence, a huge polymerization apparatus is required, andthe cost of separating the copolymer increases. The above defects can beeliminated by maintaining the concentration of the vanadium compoundwithin the above range in the polymerization system, and a copolymerhaving a low molecular weight can be produced in a high yield per unitamount of the reaction solvent despite the relatively low hydrogenpressure.

The vanadium compound is supplied to the polymerization system as asolution in a polymerization medium, preferably an inert liquid medium.The vanadium compound should not be fed in a much higher concentrationthan that in the polymerization system as in the production of ahigh-molecular-weight copolymer. The concentration of the vanadiumcompound in the solution should be 1 to 5 times, preferably 1 to 4times, the concentration of the vanadium compound present in the liquidphase of the polymerization system. If the concentration of the vanadiumcompound in the liquid phase exceeds 5 millimoles/liter, it isespecially preferred to feed it in a concentration which is not morethan 3 times the concentration of the vanadium compound in the liquidphase. If the vanadium compound is fed into the polymerization system ina concentrated form without the aforesaid dilution, a copolymer which isuniform and has a narrow molecular weight distribution is difficult toobtain.

The amount of the organoaluminum compound is such that the Al/V atomicratio in the liquid phase of the polymerization system is from 2 to 50,preferably from 3 to 20. Desirably, the organoaluminum compound is to befed to the polymerization system as a solution or dispersion in apolymerization medium, preferably an inert liquid medium, as in the caseof the vanadium compound. Unlike the vanadium compound, theconcentration of the organoaluminum compound needs not to be strictlyadjusted. For example, the concentration of the organoaluminum isadjusted to not more than 50 times the concentration of theorganoaluminum compound present in the polymerization system.

The alpha-olefin to be copolymerized with ethylene in the presentinvention preferably includes those having 3 to 20 carbon atoms, such aspropylene, 1-butene, 1-pentene, 1-hexene, 1-octene, 1-decene,1-dodecene, 1-tetradecene, 1-octadecene, 1-eicosene, and4-methyl-1-pentene. They may be used either singly or as a mixture oftwo or more. Alpha-olefins having 3 to 14 carbon atoms, such aspropylene, 1-butene, 1-hexene, 1-octene, 1-decene and 1-dodecene, areespecially preferred.

The proportions of the ethylene and the alpha-olefin to be fed to thepolymerization system vary depending upon the type of the alpha-olefinor the polymerization conditions, and cannot be generalized. They areadjusted so that the ethylene content of the resulting copolymer is from30 to 90 mole %, preferably from 35 to 85 mole %. For example, the moleratio of ethylene to the alpha-olefin is maintained at from 10:1 to1:10, preferably from 10:2 to 2:10.

The amount of hydrogen used to control the molecular weight of theresulting copolymer also varies depending upon the polymerizationconditions. In order to obtain a copolymer having a molecular weight of300 to 30,000, preferably from 500 to 25,000, the mole ratio of hydrogento ethylene+alpha-olefin is advantageously adjusted to from 1:100 to100:1, preferably from 5:100 to 100:5.

The copolymerization temperature is not critical, but is generally 0 to100° C., preferably 20 to 80° C. The polymerization pressure differsdepending upon the polymerization temperature; generally, it is from 0to 50 kg/cm² (gauge), preferably 0 to 30 kg/cm² (gauge). The averageresidence time of the polymerization mixture in the polymerizationsystem is from 5 to 300 minutes, preferably 10 to 250 minutes. Thepolymerization can be stopped by adding an alcohol, etc. in a customarymanner to the polymer solution continuously withdrawn after thereaction. The desired copolymer of ethylene and alpha-olefin isseparated from the resulting polymer solution in a customary manner by,for example, washing the polymer solution with water to remove thecatalyst residue, and then distilling it to remove the polymerizationsolvent.

The ethylene/alpha-olefin copolymer of the invention so produced is alow-molecular-weight copolymer having an ethylene content of 30 to 90mole %, preferably 35 to 85 mole %, and a number average molecularweight of from 300 to 30,000, preferably from 500 to 25,000.

The catalyst content of the copolymer, throughout the presentspecification and claims, is a value measured by ¹³ C-NMR spectroscopy.

The ethylene/alpha-olefin copolymer provided by this invention ischaracteristic in that it has a very narrow statistical molecular weightdistribution. The statistical molecular weight distribution, as referredto herein, denotes a logarithmic normal distribution, or a distributionsimilar to it, of molecular weight of the copolymer obtained directly bypolymerization from which a substantial amount, for example at least 10%by weight, of a low-molecular-weight component (and/or ahigh-molecular-weight component) has not yet been removed. Thismolecular weight distribution is defined by a Q value which is the ratioof the weight average molecular weight to the number average molecularweight and a Z value which is the ratio of the maximum value of themolecular weight to the minimum value of the molecular weight when themolecular weight is measured by gel permeation chromatography. Theethylene/alpha-olefin copolymer provided by this invention has a Q valueof not more than 3, preferably not more than 2.8, more preferably notmore than 2.6, and a Z value of from 15 to 200, preferably from 20 to190, more preferably from 30 to 180.

The number average molecular weight and weight average molecular weightof the copolymer are measured by the following method. For details ofthe method, reference may be made to Journal of Polymer Science, PartA-II, vol. 8, pages 89-103 (1970).

Elution counts of a standard substance having a known molecular weight(16 samples of monodisperse polystyrene having different molecularweights selected from the range of 500 to 840×10⁴ 0 were measured by GPC(gel-permeation chromatography), and a calibration curve showing therelation between the molecular weight and the elution count wasprepared. The GPC pattern of a copolymer sample was taken by GPC. Fromthe calibration curve, the molecular weights (Mi) at the individualcounts (i) were read, and from the PGC pattern, the elution volumes (Ni)at the individual counts (i) were read. The number average molecularweight (M_(n)) and weight average molecular weight (M_(w)), both aspolystyrene, of the copolymer sample were calculated in accordance withthe following equations.

    M.sub.n .tbd.ΣMiNi/ΣNi

    M.sub.w .tbd.ΣMi.sup.2 Ni/ΣMiNi

Separately, the molecular weight, calculated as polystyrene, of squalane(an isoparaffinic standard substance having a molecular weight of 422)was measured by GPC.

Thus, the M_(n), Q value and Z value of the copolymer of this inventionwere calculated by the following equations. ##EQU1##

The minimum and maximum elution counts of the GPC pattern of thecopolymer were read, and the corresponding minimum and maximum molecularweights of the copolymer, calculated as polystyrene, were read from thecalibration curve. The Z value was thus calculated from the followingequation. ##EQU2##

The ethylene/alpha-olefin copolymer provided by this invention is usefulin various applications according to its inherent properties, especiallyas a synthetic lubricant, a fuel oil additive or a lubricant oiladditive.

For example, copolymers of this invention having an ethylene content of30 to 70 mole %, preferably 40 to 60 mole %, and a number averagemolecular weight of 300 to 2,000, preferably 500 to 1,800, can beadvantageously used as synthetic lubricant oils.

Thus, the present invention also provides a synthetic lubricant oilconsisting substantially of a copolymer of ethylene and an alpha-olefinhaving an ethylene content of from 30 to 70 mole %, a number averagemolecular weight of from 300 to 2,000, and a molecular distributiondefined by a Q value (the ratio of the weight average molecular weightto the number average molecular weight) of not more than 3 and a Z value(the ratio of the maximum value of the molecular weight to the minimumvalue of the molecular weight when the molecular weight is measured bygel-permeation chromatography) of from 15 to 200.

In the synthetic lubricant oil of this invention, the copolymerpreferably has an ethylene content of at least 30 mole % because such acopolymer has a high viscosity index. In order to obtain goodflowability of low temperatures, the ethylene content of the copolymeris preferably up to 70 mole %.

When the copolymer of the invention is intended for use as a syntheticlubricant oil, alpha-olefins having 3 to 14 carbon atoms are preferredfor copolymerization with ethylene. In particular, lube oils consistingof ethylene/alpha-olefin copolymers containing alpha-olefins having 8 to14 carbon atoms as a constituent unit have excellent viscositycharacteristics at low temperatures.

Preferably, the ethylene/alpha-olefin copolymer used in the syntheticlubricant oil of the invention has a number average molecular weight ofat least 300 in order to obtain a high flash point and not more than2,000 in order to obtain good flowability.

For use as a lubricant oil, the copolymer may show a statistic molecularweight distribution defined by a Q value of not more than 3, preferablynot more than 2.8, and a Z value of 15 to 200, preferably 20 to 190, Ifthe copolymer has a Q value exceeding 3 at the same molecular weight, ithas the defect of possessing a lower flash point and a higher pourpoint. In order for the copolymer to have a good viscosity index inspite of its low Q value, it is important that the copolymer should havea Z value of 15 to 200, thus showing a statistic molecular weightdistribution. For example, a copolymer having a Q value of not more than3 and a molecular weight distribution curve being nearly perpendicularon the low molecular weight side and the high molecular weight side(i.e., having a Z value of not more than 15) which is obtained bysubjecting a copolymer having a large Q value to precise distillation isnot preferred because it has a low viscosity index.

The synthetic lubricant oil of this invention has a viscosity index ofgenerally at least 130, preferably at least 140, and a kinematicviscosity at 100° C. of usually 4 to 200 centistokes. Even when thelubricant oil of this invention has a kinematic viscosity at 100° C. ofmore than 60 centistokes, its flowability at low temperatures is good,and it can be suitably used as a lube oil for high loads.

The synthetic lubricant oil of this invention has an flash point of atleast 200° C.

As stated above, the synthetic lubricant oil of this invention has theadvantage of possessing a high viscosity index, excellent oxidationstability, shear stability and heat stability and high oil filmstrength. In addition, it is characterized by the fact that despite itshigh viscosity index, it has a high flash point and low pour point.

Furthermore, since the copolymer of the invention has the aforesaidproperties, it is possible to provide not only a practical syntheticlubricant oil of high viscosity for high loads but also a syntheticlubricant oil having a relatively low viscosity at low temperatures.

The synthetic lubricant oil of the invention consists essentially of thecopolymer having the aforesaid properties. If required, it may containan antioxidant, an extreme pressure agent, a cleaning dispersant, etc.and if especially desired, a flowability improver, a viscosity indeximprover, and other conventional additives in usual amounts. It may alsobe used in mixture with another lubricant oil.

Ethylene/alpha-olefin copolymers provided by this invention which havean ethylene content of 70 to 90 mole %, preferably 75 to 85 mole %,especially preferably 77 to 83 mole %, and a number average molecularweight of 1,000 to 20,000, preferably 2,000 to 20,000, especiallypreferably 3,000 to 10,000, can be used advantageously as a fuel oiladditive.

It is known that in a cold climate, distillation fuel oils generallygive rise to a problem of poor flowability in pipe lines or filtersbecause paraffins contained therein solidify, and in order to improvetheir flowability, various additives are incorporated. An ethylene/vinylacetate copolymer (EVA) is a typical example of such an additive. Theethylene/alpha-olefin copolymer of this invention is characterized bythe fact that it has excellent solubility in various fuel oils and doesnot precipitate over long periods of time, and moreover, it improves thelow temperature flowability of fuel oils, particularly the cold filterplugging point (C.F.P.P.) (described in Journal of Petroleum, Vol. 52,No. 510) of relatively heavy fuel oils.

The ethylene/alpha-olefin copolymer to be added to a fuel oil is acopolymer of ethylene and an alpha-olefin having an ethylene content offrom 70 to 90 mole %, a number average molecular weight of from 1,000 to20,000, and a molecular weight distribution defined by a Q value (theratio of the weight average molecular weight to the number averagemolecular weight) of not more than 3, preferably not more than 2.8, anda Z value (the ratio of the maximum value of the molecular weight to theminimum value of the molecular weight when the molecular weight ismeasured by gel permeation chromatography) of from 15 to 200.

Especially preferably for addition to a fuel oil, the above copolymerhas an ethylene content of 75 to 85 mole % and a number averagemolecular weight of 2,000 to 20,000.

In order to obtain an effect of imparting excellent low-temperatureflowability to fuel oils, it is especially preferred that the copolymerhave an ethylene content of at least 70 mole % and a number averagemolecular weight of 1,000 to 20,000.

It is also essential to use copolymers having a Q value of not more than3 because if the Q value is above 3, the copolymer does not dissolveuniformly in a fuel oil and partly precipitates.

Examples of fuel oils to which the copolymer of the invention is addedare straight run or cracked gas oil or a blend in any proportion ofstraight run and thermally and/or catalytic cracked distillates etc. Byuses, such fuel oils include jet fuels, kerosene, heating oils, dieselfuels, etc.

The fuel oil additive composed of the copolymer of this inventionexhibits its best effect when added to middle distillate fuel oil havinga boiling range of 170 to 400° C. and an end point of at least 360° C.

Preferably, in the fuel oil composition in accordance with thisinvention, the amount of the ethylene/alpha-olefin copolymer is 0.005 to5.0% by weight, preferably 0.01 to 1.0% by weight, based on the weightof the fuel oil.

Ethylene/alpha-olefin copolymers of this invention which have anethylene content of 50 to 90 mole %, preferably 50 to 80 mole %, and anumber average molecular weight of 5000 to 25000 are also effectivelyused as lubricant oil additives.

In addition to the aforesaid uses, the ethylene/alpha-olefin copolymersof the invention having excellent uniformity can also be used as baseoils of greases, textile finishing oils heat transfer medium oils, andthe like.

The following examples illustrate the present invention morespecifically.

EXAMPLE 1

An ethylene/propylene copolymer was synthesized continuously by using a4-liter glass reactor equipped with stirring impellers.

2 liters of hexane as a solvent, 1 liter of a hexane solution of vanadyltrichloride (16 millimoles/liter), and 1 liter of a hexane solution (96millimoles/liter) of ethyl aluminum sesquichloride were fed hourly intothe reactor from its top in a continuous manner. In the meantime, thereaction solution was continuously withdrawn from the bottom of thereactor so that the amount of the reaction solution in the reactor wasalways kept at 2 liters. A gaseous mixture of ethylene, propylene andhydrogen (50 liters/hr of ethylene, 62 liters/hr of propylene and 188liters/hr of hydrogen) was fed into the reactor from its top.) Thereaction temperature was adjusted to 35° C. by circulating hot waterthrough a jacket mounted on the outside of the reactor. A small amountof methanol was added to the reaction solution withdrawn from the bottomof the reactor to stop the reaction. Then, the reaction solution waswashed with water three times, and then distilled under a reducedpressure of 30 mmHg at a pot temperature of 100° C. to remove the hexanesolvent. There was obtained an ethylene/propylene copolymer having theproperties shown in Table 1.

EXAMPLE 2

The procedure of Example 1 was followed except that a 20millimoles/liter hexane solution of vanadyl trichloride, a 240millimoles/liter hexane solution of ethyl aluminum sesquichloride andhexane were fed respectively at a rate of 2 liters/hr, 1 liters/hr and 1liters/hr. There was obtained an ethylene/propylene copolymer having theproperties shown in Table 1.

EXAMPLE 3

The procedure of Example 1 was followed except that the amounts ofethylene, propylene and hydrogen fed were changed respectively to 62liters/hr, 42 liters/hr, and 195 liters/hr. There was obtained anethylene/propylene copolymer having the properties shown in Table 1.

EXAMPLE 4

The procedure of Example 1 was followed except that vanadiumtetrachloride was used instead of vanadyl trichloride. There wasobtained an ethylene/propylene copolymer having the properties shown inTable 1.

EXAMPLE 5

The procedure of Example 1 was followed except that vanadylethoxydichloride (VO(OC₂ H₅)Cl₂) was used instead of vanadyltrichloride. There was obtained an ethylene/propylene copolymer havingthe properties shown in Table 1.

EXAMPLE 6

The procedure of Example 1 was followed except that the amounts ofethylene, hydrogen and hexane solvent fed were changed respectively to30 liters/hr, 180 liters/hr and 1 liter/hr, and 1 liter/hr of a hexanesolution (340 g/liter) of hexene-1 was used instead of propylene. Therewas obtained an ethylene/hexene-1 copolymer having the properties shownin Table 1.

EXAMPLE 7

The procedure of Example 1 was followed except that the amounts ofethylene, hydrogen and hexane solvent were changed respectively to 36liters/hr, 180 liters/hr and 1 liter/hr, and 1 liter/hr of decene-1 wasused instead of propylene. There was obtained an ethylene/decene-1copolymer having the properties shown in Table 1.

COMPARATIVE EXAMPLE 1

The procedure of Example 1 was followed except that a 160millimoles/liter hexane solution of vanadyl trichloride as the vanadiumcompound and the hexane solvent were fed respectively at a rate of 0.1liters/hr and 2.9 liters/hr. There was obtained an ethylene/propylenecopolymer having the properties shown in Table 1.

COMPARATIVE EXAMPLE 1'

The copolymer obtained in Comparative Example 1 was dewaxed with methylethyl ketone in accordance with the method described in "Lubricant Oilsand Greases" written by Hiroshi Horiguchi, and then subjected to toppingunder a reduced pressure of 0.1 mmHg at a pot temperature of 200° C. Theresulting product oil had the properties shown in Table 1.

COMPARATIVE EXAMPLE 2

The procedure of Example 1 was followed except that 100 millimoles/literhexane solution of vanadyl trichloride as the vanadium compound and thehexane solvent were fed respectively at a rate of 0.4 liter/hr and 2.6liters/hr. There was obtained an ethylene/propylene copolymer having theproperties shown in Table 1.

COMPARATIVE EXAMPLE 3

The procedure of Example 1 was followed except that the amounts ofethylene, propylene and hydrogen fed were changed respectively to 5liters/hr, 100 liters/hr and 195 liters/hr. There was obtained anethylene/propylene copolymer having the properties shown in Table 1.

COMPARATIVE EXAMPLE 4

The procedure of Example 1 was followed except that the amounts ofethylene, propylene and hydrogen fed were changed respectively to 21liters/hr, 24 liters/hr and 225 liters/hr. There was obtained anethylene/propylene copolymer having the properties shown in Table 1.

COMPARATIVE EXAMPLE 5

An ethylene/propylene copolymer was synthesized by a batchwise method ina 2-liter glass reactor equipped with stirring impellers.

In the reactor, a hexane solution of ethyl aluminum sesquichloride (24millimoles/0.75 liter) was prepared. From the top of the reactor, ahexane solution of vanadyl trichloride (4 millimoles/0.75 liter) wasadded dropwise through a dropping funnel. Simultaneously, a gaseousmixture of ethylene, propylene and hydrogen (50 liters/hr of ethylene,62 liters/hr of propylene and 188 liters/hr of hydrogen) was fed intothe reactor, and the reaction was started. The reaction temperature wasadjusted to 35° C. by an ice water bath and a warm water bath. Thirtyminutes after the start of the reaction, a small amount of methanol wasadded to the reaction mixture from the top of the reactor to stop thereaction. The reaction mixture was then worked up in the same way as inExample 1. There was obtained an ethylene/propylene copolymer having theproperties shown in Table 1.

                                      TABLE 1                                     __________________________________________________________________________    Concent-                                                                      ration                         Kinematic                                      of the          Number         viscosity Flash                                vanadium        average-   Pour                                                                              at 100° C.                                                                  Viscosity                                                                          point                                                                            Appearance                        catalyst   Ethylene                                                                           molecular  point                                                                             (cst)                                                                              index                                                                              (° C.)                                                                    of the                            (milli-    content                                                                            weight                                                                             Q  Z  (° C.)                                                                     (*2) (*3) (*4)                                                                             copolymer                         moles/l)   (mole %)                                                                           (M.sub.n)                                                                          Value                                                                            Value                                                                            (*1)                                               __________________________________________________________________________    Example                                                                       1     4    52   960  2.6                                                                              110                                                                               -37.5                                                                            60.6 175  265                                                                              Colorless                                                                     and clear                         2     10   51   750  2.1                                                                               80                                                                               -42.5                                                                            23.5 160  240                                                                              Colorless                                                                     and clear                         3     4    64   880  1.8                                                                               80                                                                               -37.5                                                                            36.6 175  260                                                                              Colorless                                                                     and clear                         4     4    53   940  2.5                                                                              105                                                                               -37.5                                                                            58.3 175  260                                                                              Colorless                                                                     and clear                         5     4    51   950  2.6                                                                              110                                                                               -37.5                                                                            60.3 175  260                                                                              Colorless                                                                     and clear                         6     4    57   910  2.2                                                                              110                                                                               -37.5                                                                            34.7 140  240                                                                              Colorless                                                                     and clear                         7     4    44   1100 2.2                                                                              100                                                                               -47.5                                                                            33.5 172  265                                                                              Colorless                                                                     and clear                         Compartive                                                                    Example                                                                       1     4    53   970  3.6                                                                              370                                                                               -25.0                                                                            90.3 175  195                                                                              Opalescent                        1'    4    51   950  2.1                                                                               10                                                                               -35.0                                                                            62.5 155  260                                                                              Colorless                         2     10   52   890  3.8                                                                              450                                                                               -27.5                                                                            41.2 170  190                                                                              Opalescent                        3     4    10   810  2.5                                                                              100                                                                               -27.5                                                                            29.3  66  230                                                                              Colorless                                                                     and clear                         4     4    55   250  2.6                                                                               30                                                                               -60>                                                                              2.3 165  120                                                                              Colorless                                                                     and clear                         5     4    55   930  9.3                                                                              870                                                                              +100                                                                              Impossi-                                                                           Impossi-                                                                           -- Mixture of                                                       ble of                                                                             ble of  a white wax                                                      measure-                                                                           measure-                                                                              and a color-                                                     ment ment    less liquid                       __________________________________________________________________________     (*1): Measured by JIS K2269-80;                                               (*2): Measured by JIS K2283-80;                                               (*3): Measured by JIS K2283-80;                                               (*4): Measured by JIS K2265-80.                                          

EXAMPLE 8

The procedure of Example 1 was followed except that the concentration ofthe hexane solution of vanadyl trichloride was changed to 4millimoles/liter, the concentration of the hexane solution of ethylaluminum sesquichloride was changed to 24 millimoles/liter, and theamounts of ethylene, propylene and hydrogen fed were changedrespectively to 210 liters/hr, 60 liters/hr and 30 liters/hr. Theresulting copolymer had an ethylene content of 78 mole %, an averagemolecular weight of 8,200, a Q value of 2.1 and a Z value of 170. Thepolymer was added in a concentration of 5% by weight to a mineral oil(150 neutral oil having a viscosity index of 103). The resultingsolution was cleared at room temperature and had a viscosity index of162, good ultrasonic shear stability and a viscosity decrease at 210°F., measured in accordance with ASTM D-203, of 5%.

COMPARATIVE EXAMPLE 6

The procedure of Example 1 was followed except that the concentration ofthe hexane solution of vanadyl trichloride was changed to 24millimoles/liter and the amounts of the hexane solvent, ethylene,propylene and hydrogen were changed respectively to 2.9 liters/hr, 210liters/hr, 60 liters/hr, and 30 liters/hr. The resulting copolymer hadan ethylene content of 77 mole %, an average molecular weight of 8,100,a Q value of 3.7, and a Z value of 460. A solution obtained by addingthe copolymer in a concentration of 5% by weight to a mineral oil (150neutral oil having a viscosity index of 103) was opalescent at roomtemperature and was unsuitable for use as a lubricant oil.

COMPARATIVE EXAMPLE 7

The procedure of Example 1 was followed except that the concentrationsof the hexane solution of vanadyl trichloride and the hexane solution ofethyl aluminum sesquichloride were changed respectively to 2.4millimoles/liter and 14.4 millimoles/liter, and the amounts of ethylene,propylene and hydrogen were changed respectively to 180 liters/hr, 199liters/hr, and 1 liter/hr. The resulting copolymer had an ethylenecontent of 64 mole %, an average molecular weight of 50,000, a Q valueof 2.4 and a Z value of 170. A solution obtained by adding the copolymerin a concentration of 5% by weight to a mineral oil (150 neutral oilhaving a viscosity index of 103) had poor ultrasonic shear stability anda viscosity decrease at 210° F. of 20%.

COMPARATIVE EXAMPLE 8

The procedure of Example 1 was followed except that the concentrationsof the hexane solution of vanadyl trichloride and the hexane solution ofethyl aluminum sesquichloride were changed respectively to 4millimoles/liter and 24 milliliters/liters, and the amounts of ethylene,propylene and hydrogen were changed respectively to 160 liters/hr, 20liters/hr, and 120 liters/hr. The resulting copolymer had an ethylenecontent of 93 mole %, an average molecular weight of 5,400, a Q value of2.3 and a Z value of 165. The resulting copolymer was scarcely solublein middle distillate fuel (I) (initial boiling point 225° C.; end point374° C.; pour point (P.P.) 2.5° C.; cold filter plugging point(C.F.P.P.) 2° C.) at room temperature.

COMPARATIVE EXAMPLE 9

The procedure of Example 1 was followed except that the concentration ofthe hexane solution of vanadyl trichloride was changed to 40millimoles/liter and it was fed at a rate of 0.1 liter/hr; theconcentration of the hexane solution of ethyl aluminum sesquichloridewas changed to 24 millimoles/liter; and the amounts of the hexanesolvent, ethylene, propylene and hydrogen were changed respectively to2.9 liters/hr, 148 liters/hr, 32 liters/hr and 120 liters/hr. Theresulting copolymer had an ethylene content of 82 mole %, an averagemolecular weight of 5,300, a Q value of 3.8, and a Z value of 420. Asolution obtained by adding this polymer in a concentration of 0.05% byweight of middle distillate fuel (I) (initial boiling point 225° C.; endpoint 374° C.; pour point (P.P.) 2.5° C.; cold filter plugging point(C.F.P.P.) 2° C.) was opalescent at room temperature, and had a pourpoint of 2° C.

EXAMPLE 9

An ethylene/propylene copolymer was synthesized continuously by using a4-liter glass reactor equipped with stirring impellers.

Two liters of hexane as a solvent, 1 liter of a hexane solution ofvanadyl trichloride (16 millimoles/liter) and 1 liter of a hexanesolution of ethyl aluminum sesquichloride (96 millimoles/liter) werecontinuously fed hourly into the reactor from its top. In the meantime,the reaction solution was continuously withdrawn from the bottom of thereactor so that the amount of the reaction solution in the reactor wasalways kept at 2 liters (the concentration of vanadyl trichloride in thereaction: 4 millimoles/liter). A gaseous mixture of ethylene, propyleneand hydrogen (90 liters/hr of ethylene, 90 liters/hr of propylene and120 liter/hr of hydrogen) was introduced into the reactor from its top.The reaction temperature was adjusted to 35° C. by circulating hot waterthrough a jacket mounted on the outside of the reactor. A small amountof methanol was added to the reaction solution withdrawn from the bottomof the reactor to stop the reaction. The reaction solution was thenwashed with water three times, and then distilled under a reducedpressure of 30 mmHg at a pot temperature of 100° C. to remove the hexanesolvent. There was obtained an ethylene/propylene copolymer having theproperties shown in Table 2.

EXAMPLE 10

The procedure of Example 9 was followed except that the amounts ofethylene, propylene and hydrogen fed were changed respectively to 70liters/hr, 70 liters/hr and 160 liters/hr. There was obtained anethylene/propylene copolymer having the properties shown in Table 2.

EXAMPLE 11

The procedure of Example 9 was followed except that the amounts ofethylene, propylene and hydrogen were changed respectively to 53liters/hr, 52 liters/hr and 195 liters/hr. There was obtained anethylene/propylene copolymer having the properties shown in Table 2.

EXAMPLE 12

The procedure of Example 9 was followed except that the amounts ofethylene, propylene and hydrogen fed were changed respectively to 50liters/hr, 46 liters/hr and 202 liters/hr. There was obtained anethylene/propylene copolymer having the properties shown in Table 2.

EXAMPLE 13

The procedure of Example 9 was followed except that the amounts ofethylene, propylene and hydrogen fed were changed respectively to 46liters/hr, 44 liters/hr and 210 liters/hr. There was obtained anethylene/propylene copolymer having the properties shown in Table 2.

EXAMPLE 14

The procedure of Example 9 was followed except that the amounts ofethylene, propylene and hydrogen were changed respectively to 35liters/hr, 55 liters/hr and 210 liters/hr. There was obtained anethylene/propylene copolymer having the properties shown in Table 2.

EXAMPLE 15

The procedure of Example 9 was followed except that the amounts ofethylene, propylene and hydrogen were changed respectively to 55liters/hr, 35 liters/hr and 210 liters/hr. There was obtained anethylene/propylene copolymer having the properties shown in Table 2.

EXAMPLE 16

The procedure of Example 9 was followed except that the amounts ofethylene and hydrogen were changed respectively to 10 liters/hr and 270liters/hr; instead of propylene, an n-decane solution (0.5 liters/literof n-decane) of decene-1 was fed at a rate of 1 liter/hr instead ofpropylene; vanadyl trichloride and ethyl aluminum sesquichloride werefed as n-decane solutions; and that the reaction temperature wasadjusted to 50° C. There was obtained an ethylene/decene-1 copolymerhaving the properties shown in Table 2.

COMPARATIVE EXAMPLE 10

The copolymer obtained in Comparative Example 5 was distilled under areduced pressure of 0.06 mmHg in a rectifying column, and fractionsobtained at an overhead temperature of 160 to 280° C. were collected asa product oil. The GPC chart of the product oil showed a non-statisticmolecular weight distribution. The properties of the product oil werealso shown in Table 2.

COMPARATIVE EXAMPLE 11

The procedure of Example 9 was followed except that the amounts ofethylene, propylene and hydrogen were changed respectively to 18liters/hr, 22 liters/hr and 260 liters/hr. There was obtained anethylene/propylene copolymer having the properties shown in Table 2.

COMPARATIVE EXAMPLE 12

The procedure of Example 9 was followed except that ethylene, propyleneand hydrogen were changed respectively to 105 liters/hr, 105 liters/hrand 90 liters/hr. There was obtained an ethylene/propylene copolymerhaving the properties shown in Table 2.

COMPARATIVE EXAMPLE 13

The procedure of Example 9 was repeated except that the amounts ofethylene, propylene and hydrogen were changed respectively to 73liters/hr, 32 liters/hr and 195 liters/hr. There was obtained anethylene/propylene copolymer having the properties shown in Table 2.

COMPARATIVE EXAMPLE 14

The procedure of Example 9 was followed except that the amounts ofethylene, propylene and hydrogen were changed respectively to 5liters/hr, 100 liters/hr and 195 liters/hr. There was obtained anethylene/propylene copolymer having the properties shown in Table 2.

                                      TABLE 2                                     __________________________________________________________________________                                                Extreme                                                        Kinematic      pressure                                     Average    Flash                                                                            Pour                                                                              viscosity                                                                          Viscosity                                                                          Viscosity                                                                          properties                        Ethylene   molecular  point                                                                            point                                                                             at 100° C.                                                                  at -18° C.                                                                  index                                                                              (Four-ball                        content    weight                                                                             Q  Z  (° C.)                                                                    (° C.)                                                                     (cst)                                                                              (cp) (VI.sub.E)                                                                         method)                           (mole %)   (M.sub.n)                                                                          value                                                                            value                                                                            (*1)                                                                             (*2)                                                                              (*3) (*4) (*5) (kg/cm.sup.2)(*6)                 __________________________________________________________________________    Example                                                                        9    54   1500 2.5                                                                              175                                                                              286                                                                              -27.5                                                                             163  --(*7)                                                                             191  9.0                               10    55   1200 2.5                                                                              170                                                                              272                                                                              -30.0                                                                             108  --   183  8.0                               11    53   990  2.5                                                                              110                                                                              263                                                                              -35.0                                                                             49.6 --   171  8.0                               12    55   830  2.5                                                                              90 260                                                                              -45.0                                                                             21.3 --   167  6.0                               13    55   550  2.3                                                                              30 235                                                                              -55.0                                                                             7.00 --   163  5.5                               14    41   540  2.4                                                                              30 232                                                                              -55.0                                                                             6.82 --   160  5.5                               15    62   550  2.4                                                                              30 236                                                                              -52.5                                                                             7.06 900  166  5.5                               16    46   580  2.1                                                                              50 241                                                                              -50.0                                                                             7.80 760  163  6.0                               Comparative                                                                   Example                                                                       10    55   560  1.1                                                                              10 237                                                                              -37.5                                                                             6.46 2000 121  5.0                               11    53   200  2.3                                                                              30  98                                                                              below                                                                             2.31 --   161  2.5                                                        -60° C.                                       12    54   3100 2.5                                                                              170                                                                              292                                                                              +10.0                                                                             --   --   --   7.0                               13    72   830  2.5                                                                              80 260                                                                              +5.0                                                                              46.6 --   170  5.0                               14    10   810  2.5                                                                              75 230                                                                              -27.5                                                                             29.3 --    66  4.0                               __________________________________________________________________________     (*1): Measured by JIS K2265-80;                                               (*2): Measured by JIS K2269-80;                                               (*3): Measured by JIS K2283-80;                                               (*4): Measured by JIS K2215-80;                                               (*5): Measured by JIS K2283-80;                                               (*6): Measured by JIS K2519-59;                                               (*7): The symbol "--" indicates that no measurement was made.            

EXAMPLE 17

The procedure of Example 1 was followed except that the concentration ofthe hexane solution of vanadyl trichloride and the hexane solution ofethyl aluminum sesquichloride were changed respectively to 4 to 32millimoles/liter, and the amounts of ethylene, propylene and hydrogenfed were changed respectively to 140 liters/hr, 40 liters/hr and 120liters/hr. The resulting ethylene/propylene copolymer had an ethylenecontent of 79 mole %, a number average molecular weight of 4,800, a Qvalue of 2.5 and a Z value of 170.

The copolymer was added in a proportion of 0.05% by weight to a middledistillate fuel (I) (initial boiling point 225° C.; end point 374° C.;pour point (P.P.) 2.5° C.; cold fiber plugging point (C.F.P.P.) 2° C.).The P.P. and C.F.P.P. of the resulting mixture were found to be -25.0°C. and -7° C., respectively. This shows that the low-temperatureflowability of the middle distillate fuel (I) was considerably improvedby the addition of the copolymer.

The P.P. was measured in accordance with JIS K-2269, and C.F.P.P. wasmeasured by the method described in Journal of Petroleum, Vol. 52, N..510.

EXAMPLE 18

The procedure of Example 1 was followed except that the concentrationsof the hexane solution of vanadyl trichloride and the hexane solution ofdiethyl aluminum sesquichloride were changed respectively to 20 to 160millimoles/liter, and the amounts of ethylene, propylene and hydrogenfed were changed respectively to 200 liters/hr, 40 liters/hr, and 60liters/hr. The resulting ethylene/propylene copolymer had an ethylenecontent of 83 mole %, a number average molecular weight of 3,300, a Qvalue of 2.4, and a Z value of 160.

The resulting copolymer was added in a proportion of 0.05% by weight tothe same middle distillate fuel (I) as used in Example 17. The resultingmixture was found to have a P.P. of -20° C. and a C.F.P.P. of -6° C.This shows that the low-temperature flowability of the middle distillatefuel (I) was considerably improved by the addition of the copolymer. TheP.P. and C.F.P.P. were measured by the same methods as in Example 19.

EXAMPLE 19

The procedure of Example 1 was followed except that the concentrationsof the hexane solution of vanadyl trichloride and the hexane solution ofethyl aluminum sesquichloride were changed respectively to 4 and 32millimoles/liter, and the amounts of ethylene, propylene and hydrogenfed were changed respectively to 85 liters/hr, 200 liters/hr, and 15liters/hr. The resulting ethylene propylene copolymer had an ethylenecontent of 52 mole %, a number average molecular weight of 18,000, a Qvalue of 2.4 and a Z value of 175.

What is claimed is:
 1. A process for producing a copolymer of ethyleneand an alpha-olefin having an ethylene content of from 40 to 60 mole %,a number average molecular weight of from 300 to 8200 and a molecularweight distribution defined by a Q value (the ratio of the weightaverage molecular weight to the number average molecular weight) of notmore than 3 and a Z value (the ratio of the maximum value of themolecular weight to the minimum value of the molecular weight when themolecular weight is measured by gel permeation chromatography) of from15 to 200, which comprises copolymerizing ethylene with an alpha-olefinin the liquid phase in the presence of a polymerization catalystcomposed of a combination ofa soluble vanadium compound selected fromvanadium compounds of the formula

    VO(OR.sup.1).sub.n X.sup.1.sub.3-n and VX.sup.1.sub.4

wherein R¹ represents an aliphatic hydrocarbon group having 1 to 20carbon atoms, X¹ represents a halogen atom, and n is a number of from 0to 3 and an organoaluminum compound in the co-presence of hydrogen,characterized in that(a) the copolymerization is carried out in acontinuous manner, (b) the concentration of the vanadium compound in thepolymerization system is maintained at 0.3 to 30 millimoles/liter, and(c) the vanadium compound is supplied to the polymerization system as asolution in a polymerization medium in a concentration which is 1-5times the concentration of the vanadium compound in the liquid phase. 2.The process of claim 1 wherein the organoaluminum compound is selectedfrom organoaluminum compounds of the formula

    R.sup.2.sub.m AlX.sup.1.sub.3-m

wherein R² represents an aliphatic hydrocarbon group having 1 to 60carbon atoms, X₂ represents a halogen atom, and m is a number of from 1to
 3. 3. The process of claim 1 wherein the concentration of thevanadium compound in the liquid phase is maintained at 0.5 to 20millimoles.
 4. The process of claim 1 wherein the organoaluminumcompound is used in such an amount that the Al/V atomic ratio in theliquid phase is from 2 to
 50. 5. The process of claim 1 wherein theaverage residence time of the reaction mixture in the polymerizationsystem is from 5 to 300 minutes.
 6. The process of claim 1 wherein thecopolymerization is carried out at a temperature of from 0 to 100° C. 7.The process of claim 1 wherein the copolymerization is carried out at apressure of from 0 to 50 kg/cm² gauge.
 8. The process of claim 1 whereinethylene and the alpha-olefin are fed into the polymerization system sothat the ethylene/alpha-olefin mole ratio is from 1:10 to 10:1.
 9. Theprocess of claim 1 wherein hydrogen is used in an amount of 1/100 to100/1 moles per mole of the sum of the ethylene and alpha-olefin fed tothe polymerization system.